This ruler is a popular baby quilt block size; it features a 3" x 3" section of 1/8" grid markings, and a 1/2" seam allowance on 2 sides. It is used for cutting and checking half and quarter square triangles. In general, Omnigrid square rulers are used for secondary cutting of strips, and to square up finished quilt blocks. You can use it with a rotary cutter or a straight-edge blade. It has a diagonal angle line and edge markings for accurate measuring. The laser cut edges allow for smooth, deep cutting. The patented double-sight lines show up on light and dark fabrics. It is made from heavy-duty durable acrylic material with a left- and right-hand numbering and angle system.Details:6.5" x 6.5"Laser cut edgesDouble-sight linesAcrylic